Stator casing for air-cooled electrical machines

ABSTRACT

A stator casing for air-cooled machines comprises a sheet metal jacket for mounting on the stator core and having a plurality of shaped-on, axially extending, radially projecting and peripherally spaced cooling ribs. The inner surface of sheet metal jacket is axially convex, the inside edge diameters at both ends of the sheet metal jacket preferably corresponding to the outside diameter of the associated stator core. At both ends, the sheet metal jacket also has reinforcements for preventing the enlargement of the edge diameter on pressing in the stator core. The arrangement is such that upon the pressing operation, the inner surface of the jacket portions of the stator casing located between the cooling ribs are mounted so uniformly and firmly on the stator core over the entire square dimensions thereof that at least from heat and force transfer standpoints, the stator casing and stator cores substantially form a constructional unit.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a stator casing for air-cooledelectrical machines, comprising a sheet metal jacket to be placed on thestator core which has a plurality of shaped-on, axially extending,radially projecting and peripherally spaced cooling ribs.

Such a casing is already known from Swiss Pat. No. 92,809 but in thisdesign it has been found that the sheet metal jacket used therein mustbe made slightly axially longer than the stator core. The jacket thusextends axially, on either side a casing part in addition to thenon-supporting sheet metal jacket, which only serves a cooling function.

With the arrival of new technology in which the cast metal casing partscan be directly replaced by an extended sheet metal cooling rib jacket.The new jacket, however, has to be wholly or partly self-supporting, inaddition to exercising its cooling function. Such constructions, forexample Swiss Pat. No. 337,226 or West German Offenlegungsschrift No.2,233,860 are connected by means of complicated and costly welds to thestator core surface in order to obtain the necessary surface terminationor dissipation of heat and the transfer of forces.

SUMMARY OF THE INVENTION

The problem to be overcome by the present invention is to again whollyor partly move away from the welding technology and to return to thepreviously described pressing-in technology, while avoiding thedisadvantages thereof and while fulfilling the requirements of havingthe stator casing being self-supporting and with completely satisfactoryand uniform heat transfer over the entire contact surface area betweencore and casing.

According to the invention, this is achieved in that the inner surfaceof the sheet metal jacket is made axially convex and the inner edgediameters at both ends of the sheet metal jacket preferably correspondto the outside diameter of the associated stator core and that, at bothends, the sheet metal jacket has reinforcements which prevent anenlargement of the edge diameter when the stator core is pressed intothe jacket.

As a result of these measures, it is now possible that with the statorcore pressed into the stator casing the inner surface of the jacketparts of the stator casing located between the cooling ribs is uniformlyand firmly mounted on the stator core by means of its complete squaredimensions that stator casing and stator core substantially form asingle unit, in which an optimum heat transfer is ensured and the statorcasing completely fulfils the requirement of then being self-supporting.

The convex construction of the stator casing represents an initialstressing which, on pressing in the stator core ensures that the statorcasing exerts on the stator core an adequate contact pressure, which isuniformly distributed over the complete square dimensions of contact.

The reinforcements located close to the edges and which prevent anenlargement of the internal edge diameter of the stator casing onpressing in the stator core can be external and/or internal thrustrings, which are connected to the sheet metal jacket in the vicinity ofthe edge, e.g. by means of welds. These thrust rings can then serve assupports for the bearing brackets of the machine.

However, it is also possible for the reinforcements to be formed bywelded joints, close to the edges, on the base of the cooling ribs.

The present invention also relates to a use of the stator casingaccording to the invention on an air-cooled electrical machine,characterised in that the stator casing is pressed onto the stator corein such a way that the inner surface of the jacket parts located betweenthe cooling ribs is mounted so uniformly and firmly on the stator coreby the complete square dimensions thereof that stator casing and statorcore, at least from the heat and force transfer standpointssubstantially form a constructional unit.

According to a preferred development, an additional, axially extendingkeyed joint is provided between stator casing and stator core forproducing a radial form-locking action.

It is then advantageous if the machine supports are at least partlywelded through the stator casings to the stator core.

Exemplified embodiments of the invention are described hereinafterrelative to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1a is a stator casing with a stator in axial section;

FIG. 1b is an exploded view of a stator casing and a stator in axialsections;

FIG. 2 is a stator casing with thrust rings in axial section;

FIGS. 3 and 4 are front views of two different embodiments of statorarrangements of an air-cooled electrical machine;

FIG. 5 is a sectional view of a support structure on a stator casing andcore arrangement shown in part; and

FIGS. 6, 7 and 8 are fragmentary views showing keyed joints between astator casing and a stator core.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1a and 1b diagrammatically shows an arrangement of a stator casing1 with a stator core 2 as used for the stator of an inner-cooledelectrical machine, for example in accordance with the embodimentsillustrated in FIGS. 3 and 4, whereby the stator is supported on thefoundation by a support structure 15. It can also be gathered from FIGS.3 and 4 that the stator casing 1 comprises a sheet metal jacket with aplurality of shaped-on, axially extending radially projecting andperipherally spaced cooling ribs 6, 6' and between the latter areprovided jacket parts 7, 7' for engagement on the stator surface in themanner to be described in greater detail hereinafter. The cooling rib 6can be of the open form (FIG. 3) or the closed form (FIG. 4 at 6'), asis generally known and used.

For the assembly of stator casing 1 as stator core 2, core 2 is pressedinto the preshaped stator casing 1 (FIG. 1b). According to theinvention, the inner jacket surface of sheet metal jacket 1 is madeaxially convex while the inside edge diameters at both ends of thejacket 1 correspond to the external diameter of the stator core 2. Atboth ends, sheet metal jacket 1 is provided with reinforcements, to bedescribed in greater detail hereinafter, which prevent an enlargement ofits edge diameter when the stator core 2 is pressed into sheet metaljacket 1. The preshaped stator casing 1 therefore has an initialstressing, so that when core 22 is pressed in, the inner surface of thejacket portion 7 located between the cooling ribs 6, is engaged on thesurface of the stator core 2 in an absolutely uniform and firm mannerwith given contact pressure over the entire square dimensions thereofand as a result, the requirements concerning the heat transfer capacityand torque absorption are fulfilled to a predetermined extent. Thistechnology also permits a disassembly and reassembly between statorcasing 1 and stator core 2.

According to FIG. 1b, the reinforcement can be welding spots 16, closeto the edge and on the base or over the entire height of cooling ribs 6.According to FIG. 2, the reinforcement are formed by an outer thrustring 4 and an inner thrust ring 5 and naturally there can also be eithertwo outer or two inner thrust rings. These thrust rings simultaneouslyserve as supports for the bearing brackets of the machine (not shown).

FIG. 5 shows that for fitting the support structure 15 it isadvantageous to omit a cooling rib on the periphery of stator casing 1and to weld the machine support to the stator core, appropriatelythrough the stator casing 1. This naturally only forms one of a largenumber of possibilities for constructing and fitting support structures.

For larger machines, it is often advantageous to provide an additional,axially extending keyed joint between stator casing 1 and stator core 2for producing radial form locking. FIGS. 6, 7 and 8 show such joints. Inthe arrangement according to FIG. 6, axially extending flat section bars8 are distributed over and welded to the periphery of stator core 2. Onassembly, said bars engage in the appropriate open cooling rib 6 and cansimultaneously serve to hold together the individual laminations of thestator core. This keyed joint is used for axial guidance purposes duringassembly and prevents relative displacement between stator casing andstator core. In the arrangement according to FIG. 7, the flat sectionbars 9 engage both in a corresponding slot 17 in stator core 2 and in arelevant open cooling rib 6 on stator casing 1. Flat section bar 9 canbe welded to cooling rib 6. In the arrangement according to FIG. 8,section cams 10 project from stator core 2 and can engage incorresponding hollow cooling rib 6 in stator casing 1.

The above-described stator casing is generally shaped from a metalsheet, the cooling ribs being constructed mechanically by stamping orpunching tools. As a result of the appropriate curvature of these tools,it is now possible to produce the above-described convexity of the innerjacket surface in the same operation.

I claim:
 1. A stator assembly comprising:an initialy axially convexsheet metal jacket having an inside diameter near its center which isinitially smaller than an inside diameter near the jacket ends, saidjacket formed of a plurality of shaped, axially extending, radiallyprojecting and peripherally spaced cooling ribs; reinforcement means atsaid jacket ends for preventing an enlargement of diameter of saidjacket ends; and a stator core having an outside diameter substantiallythe same as said jacket inside diameter at said jacket ends, press-fitinto said jacket and against the center of said jacket to move saidcenter radially outwardly so that said stator core is firmly engagedwith said jacket and supported thereon; said reinforcement meanscomprising an outer thrust ring and an inner thrust ring connected toeach of said jacket ends by welds.
 2. A stator assembly according toclaim 1, wherein each of said ribs has an axial base adjacent eachjacket end.
 3. A stator assembly according to claim 1, wherein saidouter and inner thrust rings form supports for a bearing bracket forsupporting said stator assembly.
 4. A stator assembly according to claim1 wherein said stator core comprises the stator core of an air cooledelectric machine, said sheet metal jacket including jacket partsconnected between adjacent cooling ribs, said jacket parts uniformly andfirmly bearing against an outside diameter of said stator core along theentire area of said jacket parts so that said jacket and stator corecomprise a single heat and force transfer constructional unit.
 5. Astator assembly according to claim 4, including at least one machinesupport welded to said stator core, at least partly through said jacket.